Acyclovir is an antiviral medication used to treat herpes virus infections. It works by stopping the virus from replicating in the body. While it is generally considered safe and effective, there are some risks associated with prolonged use of acyclovir [2].

One of the most common side effects of acyclovir is nausea and vomiting. This can be especially problematic for patients who are taking the medication for a long period of time [3]. In addition, acyclovir can cause diarrhea, headache, and dizziness [2].

Another potential risk of prolonged acyclovir use is the development of drug-resistant strains of the herpes virus. This can occur when the virus mutates and becomes resistant to the medication [1].

Long-term use of acyclovir has also been associated with kidney damage. Patients with pre-existing kidney problems may be at higher risk for this side effect [2].

Finally, acyclovir can interact with other medications, including probenecid and cimetidine. Patients who are taking these medications should be closely monitored by their healthcare provider [3].

In conclusion, while acyclovir is generally considered safe and effective for the treatment of herpes virus infections, there are some risks associated with prolonged use. These risks include nausea and vomiting, the development of drug-resistant strains of the virus, kidney damage, and interactions with other medications. Patients who are taking acyclovir for an extended period of time should be closely monitored by their healthcare provider [2][3].

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/ACYCLOVIR
[2] https://www.healthline.com/health/drugs/acyclovir-oral-tablet
[3] https://www.drugs.com/sfx/acyclovir-side-effects.html